The present invention relates generally to power conversion systems for generating electricity from a power plant (coal-fired, nuclear, etc.), and more specifically to a very high efficiency (68–76%) system for converting heat generated by a high-temperature helium gas cooled nuclear reactor (HTGR) into electricity, where liquefied natural gas (LNG) is used as the cold heat sink media in a modified, closed-loop Brayton cycle, instead of conventional water or air. This improvement is due to the large temperature difference (1010 degrees) between the helium gas coolant (850 C) and LNG (−160 C). With such a large temperature difference, a Carnot thermal efficiency can theoretically approach 90%. Achievable efficiencies are in the range of 68–76%, roughly double that of 35% for conventional steam cycle power plants, and larger than 48% for current HTGR designs cooled with ambient air or water. An added benefit is that the LNG is converted to pressurized natural gas at close to ambient temperature, ready to be used by consumers, with significantly reduced costs for revaporizing the LNG. By using this synergistic system, the energy originally expended into liquefying the natural gas prior to shipping overseas can be efficiently recovered. Ideally, the LNG receiving terminal is co-located close to the power plant to eliminate the need to transport LNG overland.